The present invention relates to a tubular motor-speed reducer for the simultaneous driving of two structures which is more particularly adapted to the control of the displacements of either one of the two parts of an automobile seat structure. Each of these movements is usually controlled by two devices placed laterally under the seat structure which must be displaced simultaneously and exactly in the same way so that the transmission between the motor and these devices is often complex and even bulky. Now, it is increasingly necessary to have available under the seat structure of the vehicle a free space for increasing the comfort of the passengers.